I have a 97 F250 with a simple slip in K&N and a 3" aftermarker downpipe. My truck still runs fine. But as of 2 weeks ago and previous, I was getting 17.5 mpg. Then suddenly it only gets 14.5 mpg. Same drive, same driver. I don't understand. It has only gotten worse since the temp dropped here in Georgia. I am kinda new to diesel's, but I am a drag boat mechanic ( for lack of better terms) and it seems to me that cooler denser air would add to fuel economy not hurt. Does anyone have any suggestions as to why this might be. I am still running the same brand diesel as well. Thanks for any input. Oh and by the way. I would buy a DMax but they are still out of a "normal" working mans budget.

I would check the fuel filter. May want to check the FPR screen while the filter is out. Also how long since the last service. The injectors run off oil so it'll effect how it runs. Also if you fuel station has started using a winter blend fuel it'll cause the milage to go down.

I installed a new filter about 2 months ago. The filter media is still clean. And as for the oil, I change it every 3k miles, even though international says every 5k will suffice. But the FPR screen, once i have the filter out. Where is it in the housing? Alls I see is a metal bottom with 3 little "washers" and a rubber piece with a metal coil coming off.

its winter time, winter blend fuel, my truck does the same.

To what extent is fuel winter blended in Georgia?

The FPR screen is about a third of the way down on the drivers side inside the bowl. About a 3/8-1/2 inch hole that has a screen tucked inside it. You can try to clean it in the bowl or pull the two bolts on the FPR and it'll come apart from the filter housing. Just don't drop the screen or the little oring into the valley, ya won't find it! I know.....LOL